People carry the coffin of Fehmi Karaca, 69, a shop owner and one the victims killed in Saturday explosions, for burial in Reyhanli, near Turkey's border with Syria on Sunday. / Burhan Ozbilici, AP

by Oren Dorell, USA TODAY

by Oren Dorell, USA TODAY

Nine Turkish citizens believed to have links to the Syrian intelligence agency have been detained in connection with twin car bombings that shattered a Turkish border town, officials said Sunday, as Syria rejected allegations it was behind one of the deadliest attacks in Turkey in years.

The bombings left 46 people dead and marked the most serious incident of violence across the border since the start of Syria's bloody civil war, raising fears of Turkey being pulled deeper into the conflict.

Harsh accusations from both sides signaled a sharp escalation of already high tensions between the two former allies, with Turkey vowing a strong response and Syria branding Turkey's prime minister "a butcher."

"This incident was carried out by an organization â?¦ which is in close contact to pro-regime groups in Syria and I say this very clearly, with the Syrian mukhabarat," said Turkish Interior Minister Muammer Guler. He did not name the organization.

Among the nine people detained overnight was the mastermind of the attack and more were expected, Guler said.

"We have determined that some of them were involved in the planning, in the exploration and in the hiding of the vehicles," he said.

Deputy Prime Minister Besir Atalay said Turkish authorities determined that the nine were involved through their "testimonies and confessions," but did not elaborate during a joint press conference in Hatay, near the border town of Reyhanli where the bombs struck.

On Saturday, Secretary of State John Kerry condemned the bombings.

"This awful news strikes an especially personal note for all of us given how closely we work in partnership with Turkey," Kerry said. "Our thoughts are with the wounded and we extend our deepest condolences to the families of the victims."

One of the car bombs exploded outside a city hall while the other went off outside the post office in Reyhanli, a main hub for Syrian refugees and rebel activity in Turkey's Hatay province. Images showed people frantically carrying victims through the rubble-strewn streets to safety.

"We know that the Syrian refugees have become a target of the Syrian regime," Deputy Prime Minister Bulent Arinc said. "Reyhanli was not chosen by coincidence."

"Our thoughts are that their mukhabarat (Syrian intelligence agency) and armed organizations are the usual suspects in planning and the carrying out of such devilish plans," he said.

Arinc said Turkey would "do whatever is necessary" if proven that Syria is behind the attack.

Tanir, who visited the town in August, said it is walking distance from the Syrian border town of Idlib. It has been the scene of recent clashes between long-term residents and Syrian refugees who have flooded the town since civil war erupted in Syria two years ago, he said.

It is a mostly Sunni Muslim town in Hatay province, where a half-million residents share the Alawite Muslim sect of Syria's ruling clan. In recent months there have been protests in Hatay against Turkey's rulling party, the Justice and Development Party (AKP), he said.

Violent spillover from Syria has been limited so far, Tanir said, considering that up to 500,000 refugees have streamed into Turkey, including some who are thought to be Syrian intelligence agents.

The attack comes about a week after Israeli airstrikes reportedly destroyed a shipment of Iranian missiles destined for the Lebanese terror group Hezbollah. Tanir said the timing is similar to a car bombing Feb. 11 that Turkish intelligence officials tied to Syria's Assad regime after the last Israeli airstrike in January.

That bombing, at Cilvegozu, killed 12 people and injured 28 on the Turkish side of a rebel-held Syrian border crossing, according to the New York Times. The previous Israeli airstrike occurred on Jan. 30.

"It's a pattern, it doesn't mean a definite link," Tanir said.

Prime Minister Recep Tayyip Erdogan earlier also raised the possibility that the bombings may be related to Turkey's peace talks with Kurdish rebels meant to end a nearly 30-year-old conflict.

Syrian mortar rounds have fallen over the border before, but if the explosion turns out to be linked to Syria it would be by far the biggest death toll in Turkey related to its neighbor's civil war.

Syria shares a more than 500-mile border with Turkey, which has been a crucial supporter of the Syrian rebel cause. Ankara has allowed its territory to be used as a logistics base and staging center for Syrian insurgents.

"Those who for whatever reason attempt to bring the external chaos into our country will get a response," he said.

The main Syrian opposition group, the Syrian National Coalition, condemned the "terrorist attacks" in Reyhanli, saying it stands together with the "Turkish government and the friendly Turkish people."

The coalition sees "these heinous terrorist acts as an attempt to take revenge on the Turkish people and punish them for their honorable support for the Syrian people," it said.

Reyhanli is a center for aid and alleged weapon trafficking between Turkey and Syria, as well as for Syrian rebel activity. Apart from refugees living in camps, many Syrians escaping the civil war have also rented houses in the town.

The explosions came days before Erdogan is scheduled to travel to the U.S. for talks, which are expected to be dominated by the situation in Syria.

"This â?¦ will increase the pressure on the U.S. president next week to do something to show support to Turkey when Erdogan visits him in Washington," said Soner Cagaptay, an expert on Turkey at the Washington Institute. "Washington will be forced to take a more pro-active position on Syria, at least in rhetoric, whether or not there is appetite for such a position here."

Abdullah, a Reyhanli resident, told the Associated Press he heard two strong explosions at about 1 p.m. "The bombs were very powerful," he said by telephone.

The frontier area has seen heavy fighting between rebels and the Syrian regime. In February, a car bomb exploded at a border crossing with Turkey in Syria's Idlib province, killing 14. Turkey's interior minister has blamed Syria's intelligence agencies and its army for involvement.

Four Syrians and a Turk are in custody in connection with the Feb. 11 attack at the Bab al-Hawa frontier post. No one has claimed responsibility, but a Syrian opposition faction accused the Syrian government of the bombing, saying it narrowly missed 13 leaders of the group.

In that bombing, most of the victims were Syrians who had been waiting in an area straddling the frontier for processing to enter Turkey.

Tensions flared between the Syrian regime and Turkey after shells fired from Syria landed on the Turkish side, prompting Germany, the Netherlands and the U.S. to send two batteries of Patriot air defense missiles each to protect their NATO ally.